The increasing pollution of the human natural environment has been becoming a growing problem, which, if unsolved, will negatively influence longevity and the quality of life. The pollution of water, particularly drinking water, is of immense importance, since quite soon it may become a factor limiting the growth of human civilization, both on global scale and on the scale of particular states, especially those already lacking water.
On one hand, the development of an universal and inexpensive method of water purification is desired, however, on the other hand, it is extremely difficult taking into account the variety of types of water pollutants, e.g. heavy metals, organic compounds (pesticides, chlorinated aromatic pollutants, antibiotics, surfactants), and bacteria.
The methods of water purification are very diverse. They are based on processes such as reverse osmosis, ion exchange, adsorption, ultrafiltration, distillation, and photooxidation. The majority of them, however, have limitations, mainly high energy consumption and low efficiency.
The photocatalytic method of water purification is applied since 70s. Its primary advantage is the use of renewable and environmentally safe solar energy. As opposed to other methods, which are based on the transfer of the pollutants from one medium to another, the photocatalytic method of water purification leads to the transformation of the pollutants into harmless compounds. It is also a quite universal method, which may be applied for the detoxification of various types of pollutants. Usually it involves application of semiconductors based on TiO2, although those containing ZnO, Fe2O3, CdS, and ZnS are also studied. These photocatalysts are used in photocatalytic oxidation of organic water pollutants, although the mechanisms of their actions are known which are based on the reductive degradation of these pollutants and the removal of heavy metals. Their disadvantage, however, is the fact that most of the reactions they photocatalyze require irradiation with ultraviolet light.
The layered aluminosilicates are known such as kaolinite, montmorillonite (bentonite) mica, and talc. These minerals are composed of layers of joined tetrahedral SiO4 groups. The layer of tetrahedral SiO4 groups is combined with the layer of Al3+ ions coordinated with six oxygen atoms forming octahedral groups. The layers are arranged in parallel forming piles. The transverse dimension of a layer is several hundred of nanometers, and the distance between them is about 1 nm, therefore these minerals are also termed nanoclays. Since a part of Al3+ ions is replaced with ions with a lower positive charge (Mg2+, Fe2+), the layer has a negative charge which is neutralized with the ions occupying the space between layers (so called galleries), such as Na+, Li+, Mg2+, or Ca2+. These ions can be easily exchanged into other cations through ion exchange. Exchanging them with organic cations such as cationic surfactants leads to organically modified clays (organoclays), e.g. organically modified montmorillonite, such as commercially available Cloisite 30B. The organoclays have very low surface energy, therefore the polymeric chains and the monomer molecules may easily intercalate between organoclay layers. In the case of polymers only hydrophilic polymers may intercalate the layers of unmodified montmorillonite.
The synthesis of the photocatalysts by intercalation of a low molecular chromophore between the layers of the aluminosilicate was reported. The phthalocyanines intercalated into organically modified bentonite were applied for the oxidation of phenol (“Photosensitized oxidation of substituted phenols on aluminum phthalocyanine-intercalated organoclay” Environ. Sci. Technol. 2005, 39(2), 651-657), laponite containing an introduced chromophore which is a complex of bipyridine and Fe2+ ions applied for the degradation of organic pollutants (“Photocatalytic degradation of organic pollutants catalyzed by layered iron(II) bipyridine complex-clay hybrid under visible irradiation,” Cheng, M.; Ma, W.; Chen, C.; Yao, J.; Zhao, J. Appl.Catal. B: Environ. 2006, 65(3-4), 217-226), organically modified bentonite containing sulfonated derivative of palladium phthalocyanine was applied for the degradation of 2,4,6-trichlorophenol (“Enhanced photodegradation of 2,4,6-trichlorophenol over palladium phthalocyaninesulfonate modified organobentonite,” Xiong, Z.; Xu, Y.; Zhu, L.; Zhao, J. Langmuir 2005, 21(23), 10602-10607) and montmorillonite containing iron ions which, under irradiation, produced hydroxyl radical able to oxidize benzene (“Photochemical formation of hydroxyl radicals catalyzed by montmorillonite,” Wu, F.; Li, J.; Peng, Z.; Deng, N. Chemosphere 2008, 72(3), 407-413). These photocatalysts, however, contain heavy metals, which may pass into the environment. In the case of photocatalytic method of water purification this is a disqualifying disadvantage.
Layered aluminosilicates have many different applications. One of them is the modification of polymer properties. The first hybrid polymer-aluminosilicate hybrid materials were obtained in 1986 within the Toyota Central Research and Development Laboratories, Inc.'s (TCRDL) research project (“The discovery of polymer-clay hybrids,” Kawasumi, M. J.Polym.Sci. Part A: Polym.Chem., 2004, 42, 819-824). These studies have shown that even a slight addition of an aluminosilicate to the polymer causes significant improvement of thermal and mechanical properties of the polymer. The studies on hybrid polymer-aluminosilicate hybrid materials are very intensive. However, till now there are no hybrid materials described containing polymers which are photocatalysts.